The present invention relates to a plug-in coupling for fluid systems, having two coupling parts connectable to one another, which have coordinated catches for connection with each other. One of the coupling parts has an end union section, by means of which it can be plugged into the other coupling part, and one of the coupling parts has at least one end retaining section carrying its catches, by means of which section it grips over an outer peripheral contour of the other coupling part, on which the coordinated complementary catches are formed.
Such a coupling is described in DE 38 43 995 C1, which desired a quick-fit connector for the connection or attachment of a hose or pipe. The known connecting arrangement has a housing part (first coupling part) and a core part (second coupling part), which can each be firmly connected at one end to a hose, pipe or appliance. A seal is arranged between the core part and the housing part. In the housing part, on the one hand, a union is formed for engagement in the core part, the outside diameter thereof being slightly smaller than the open inside diameter of the core part. On the other hand, an inside diameter of a socket-like section (retaining section) of the housing part is larger than the outside diameter of the core part. At the free end of the inside wall of the socket-like section of the housing part at least two diametrically opposing cams are formed with contact faces directed towards the free end and stop faces opposite these. Each stop face runs perpendicular, or inclined, in the form of an undercut to the longitudinal axis of the housing part. The clear distance between the cams is approximately equal to the outside diameter of the core part. The housing part is composed of an elastic material, the cams being formed on a ring provided with two legs. The cams thus formed constitute catches for locking the housing part to the core part. A ring with a contact face directed towards the free end of the core part and with a stop face opposite this, which runs perpendicular or inclined in the form of an undercut to the longitudinal axis of the core part and is formed on the outside of the core part. The ring thus formed constitutes a catch, designed to complement the cams, for locking the core part to the housing part. Among the advantages of this known quick-fit connector is that it comprises only two parts with associated sealing rings and does not contain any additional parts which require assembling and which can be lost. After joining the parts of the quick-fit connector together, it is possible to turn these parts in relation to one another, although for certain applications this cannot be regarded as advantageous. In order to release the connection, a fork with tapered prongs can be inserted between the legs on the housing part and the ring on the core part so that the legs are pressed radially outward, with the result in turn that the cams are raised over the outside diameter of the ring on the core part, so that the two coupling parts can be detached from one another by pulling them apart. The need to use such a special tool likewise cannot be regarded as advantageous for many applications. However, the direct locking of the two coupling parts to be joined together does constitute an advantage in ensuring a secure and stable connection.
A similar quick-fit connector to that described above is also disclosed by the German utility model DE 87 11 334 U1. This known quick-fit connector also has a core part and housing part which can each be firmly connected at one end to a hose, pipe or appliance, a sealing ring being arranged between the core part and the housing part. Similarly, a ring with a contact face directed towards the free end and with a stop face opposite this is formed on the outside of the core part, the inside diameter of the housing part being greater than the outside diameter of the core part, at least two diametrically opposing cams with contact faces directed towards the free end and stop faces opposite these are formed on the free end of the inside wall of the housing part, the clear distance between the cams is approximately equal to the outside diameter of the core part, and the housing part is composed of an elastic material. In contrast to DE 38 43 995 C1, however, the housing part does not have an inner union for engagement in the core part. The housing may be of elliptical or oval shape in the area of the cams, the cams being arranged on the minor axis of the ellipse. The cams can thereby be made to lift from the catch position by compressing the elliptical or oval housing in the direction of the major axis of the ellipse in order to release the connection. Here too, the fact that the quick-fit connector comprises only two parts with associated sealing rings is cited as one of the advantages of the quick-fit connector since a quick-connect coupling using an additional locking part, which might get lost, as is described in DE 31 43 015 A1, would not lend itself to automated assembly. The fact that external pressure applied to the housing can in itself lead to accidental detachment of the joined parts is, however, to be seen as a disadvantage.
A similar plug-in connector to that mentioned in DE 31 43 015 A1 that is a technical solution with a separate retaining part and without a direct locking of the first and second coupling parts, is also described in DE 43 00 037 C1. The detachable plug-in connector disclosed in this specification serves to accommodate a tubular plug-in part (first coupling part) having a peripheral retaining rib. The plug-in connector in this case comprises a cylindrical socket housing (second coupling part) with a central socket chamber for the insertion of the plug-in part, and a separate spring element made from hard elastic plastics which is provided with inwardly curving, flexibly expandable retaining edges for gripping behind the retaining rib once the plug-in part has been pressed in. In order to assemble this before the plug-in part can be inserted, the spring element must be compressed and introduced through a lateral opening in the socket housing into the socket chamber. Once the spring element has re-expanded in the socket chamber, especially in the closed position, the retaining edges are axially fixed by way of guide elements which are sunk in recesses situated in the outer wall. On the insertion side for the plug-in part, the retaining edges have contact faces converging obliquely in the insertion direction, by means of which they are forced further apart on insertion of the plug-in part. In order to release the connection between the retaining edges of the spring element and the retaining rib of the plug-in part again, i.e. in order to be able to press the retaining edges radially slightly away from the retaining rib, the retaining edges at their ends are interconnected by way of spring ribs converging in a V-shape, the joints in each case being arranged in the area of an opening in the socket housing, it being possible to press these joints inwards inward by means of curved pressure tabs.